The consequences of slave trading were very different for most people in Africa than they were for most people in America. The people in America (other than, of course, the slaves) generally benefitted from the slave trade. The people in Africa were generally harmed by it even if they themselves were not taken as slaves.
African states were often badly hurt by the slave trade. This was mainly true of the states away from the coast. The coastal states did not lose that many people to slave trading. Instead, they raided inland, took slaves, and sold them to the European slave traders. This badly harmed the inland states because the people taken as slaves were typically the people in the prime of life. This was done because those people were the ones who would get the highest prices when sold. That meant that the inland states were losing the labor of the strongest members of society. They were being culturally and socially harmed by having large numbers of people torn away from them. The slave trade was devastating to them.
By contrast, the Americas generally benefitted. The plantation owners in the South, of course, benefitted from the slave labor that worked their plantations and made them rich. But the rest of the country benefitted as well. Ship owners in New England profited when their ships were used to carry slaves to the Americas. The profited from the goods they sold to Africa to get the slaves. Other companies in the North profited by doing things like insuring slaves and slave ships. They profited by selling things like shoes for the slaves to the plantations.
In these ways, the people in America generally benefitted from the slave trade while many African states were badly harmed.